+CREG?|+CGREG?|+CEREG? AT Commands return empty response.
The +CREG?|+CGREG?|+CEREG? AT commands all return an empty response when using either mmcli, or the dbus interface directly. MM debug does show the reply from the modem.
I haven't seen any other AT commands yet that also fail to return the modem's reply.
MM: v1.10.4 and v1.12.4
Modem: Sierra Wireless EM7511
From mmcli:
$ sudo mmcli -m 0 --command='+cereg?'
response: ''
From MM debug:
ModemManager[6181]: <debug> [1579983528.776145] (ttyUSB2) device open count is 2 (open)
ModemManager[6181]: <debug> [1579983528.776235] (ttyUSB2): --> 'AT+cereg?<CR>'
ModemManager[6181]: <debug> [1579983528.789033] (ttyUSB2): <-- '<CR><LF>+CEREG: 0,1<CR><LF><CR><LF>OK<CR><LF>'
ModemManager[6181]: <debug> [1579983528.789306] (ttyUSB2) device open count is 1 (close)